There is conventionally known an electric power converter which includes a plurality of switches and performs DC to AC power conversion. Such electric power converter employs on/off control of the plurality of switches to convert a DC voltage supplied from a DC power source to an AC voltage which is output.
Japanese Patent Application Laid-open No. 2006-14591 for example describes an electric power converter in which one of a plurality of upper and lower switches included in a single-phase bridge circuit is controlled by a frequency of an AC voltage, and the other of the upper and lower switches is controlled by a frequency higher than the frequency of the AC voltage.
Such electric power converter is provided with a switch connecting a anode of a DC power source and the single-phase bridge circuit, where the switch is turned off in a circulation mode to prevent potential change of high frequency from being applied to the side of the DC power source.
However, there occurs a state where the DC side and the AC side are electrically separated from each other in the electric power converter described in Japanese
Patent Application Laid-open No. 2006-14591, thereby causing a problem that a common mode voltage of the DC power source becomes inconstant.